Note that the rich content may be directly rendered instead of syntax highlighted. This usually depends on which auxiliary packages are installed and on which components are activated in your setup. For example a text/x-rst document will be rendered via docutils if it is installed and the trac.mimeview.rst.ReStructuredTextRenderer is not disabled, and will be syntax highlighted otherwise.

In a similar way, a document with the mimetype text/x-trac-wiki is rendered using the Trac wiki formatter, unless the trac.mimeview.api.WikiTextRenderer component is disabled.

HTML documents are directly rendered only if the render_unsafe_html settings are enabled in the TracIni (those settings are present in multiple sections, as there are different security concerns depending where the document comes from). If you want to ensure that an HTML document gets syntax highlighted and not rendered, use the text/xml mimetype.